Study on chemical kinetics of Na2SO4 formation in coal fired flue gas

doi:10.11949/j.issn.0438-1157.20180051

Abstract

Abstract:

The formation of gaseous sodium sulphate during Zhundong coal combustion leads to a series of problems such as the deposition and corrosion of heat exchange surface and the deactivation of tail SCR catalyst. Therefore, the kinetic study on the transformation of Na₂SO₄ is important for predicting and controlling the Na₂SO₄ formation in coal-fired flue gas. In this study, a more complicated chemical kinetic model of Na/Cl/S/O/H in flue gas was established and the formation mechanism of Na₂SO₄ was studied. The influence of oxygen content, temperature, SO₂and H₂O concentrations on Na₂SO₄ formation was also investigated. The model predictions were in good agreement with the experimental results. Oxygen promoted the formation of Na₂SO₄. Even though the chemical reactions were accelerated at high temperature, the Na₂SO₄ formation was inhibited. The effects of SO₂ and H₂O on Na₂SO₄ formation depended on reaction temperature. The path analysis indicated that there were two important paths to form Na₂SO₄:(1) the direct oxidation of SO₂ (NaCl→NaSO₃Cl→NaHSO₄→Na₂SO₄), and (2) the indirect oxidation of SO₂(NaCl→NaO₂→NaSO₄→NaHSO₄→Na₂SO₄). The result of sensitivity analysis showed that the Na₂SO₄ formation was sensitive to the reactions that generated or consumed radicals in the system.

Key words: Zhundong coal, alkali metal, Na₂SO₄ formation, chemical kinetics, reaction path

摘要：

准东煤燃烧过程中Na₂SO₄的形成会造成锅炉受热面沾污、尾部SCR催化剂失活等问题。烟气中Na₂SO₄形成及转化规律的研究对于预测和控制燃煤烟气中Na₂SO₄的形成有重要意义。发展了烟气中Na/Cl/S/O/H化学动力学模型，研究了烟气中Na₂SO₄的生成过程及转化机理，考察了含氧量、温度、SO₂浓度、H₂O浓度等因素对Na₂SO₄生成的影响。动力学计算结果表明，模型预测结果与实验数据吻合较好，验证了模型的准确性。烟气中的高氧气含量有利于Na₂SO₄的生成。高温加快化学反应的同时，抑制了Na₂SO₄的生成。SO₂和H₂O的影响效果受温度影响较大。反应路径分析表明，Na₂SO₄的生成路径有两个：一是依赖于SO₂直接氧化（NaCl→NaSO₃Cl→NaHSO₄→Na₂SO₄），二是依赖于SO₂间接氧化（NaCl→NaO₂→NaSO₄→NaHSO₄→Na₂SO₄）。敏感性分析结果表明，Na₂SO₄的生成主要对系统中生成或消耗自由基的反应更为敏感。

关键词: 准东煤, 碱金属, Na₂SO₄生成, 化学动力学, 反应路径

CLC Number:

TK16

ZHANG Zhichao, LIU Jing, YANG Yingju, ZHANG Zhen. Study on chemical kinetics of Na₂SO₄ formation in coal fired flue gas[J]. CIESC Journal, 2018, 69(8): 3643-3650.

张志潮, 刘晶, 杨应举, 张振. 燃煤锅炉烟气中Na₂SO₄生成的化学动力学研究[J]. 化工学报, 2018, 69(8): 3643-3650.

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Study on chemical kinetics of Na₂SO₄ formation in coal fired flue gas

燃煤锅炉烟气中Na₂SO₄生成的化学动力学研究

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